This invention relates to hand operated rotary electric tools and particularly to an automatic brake control for said tools. The prior art includes a number of patents which in general disclose armature brakes for electric motors. Of particular interest is my U.S. Pat. No. 4,029,159 which discloses an electric tool wherein a solenoid mechanism is wired to the trigger switch and is activated thereby, causing a cam to move the brake shoes out of engagement with the brake drum during operation. When the trigger is released, the solenoid is deactivated, permitting the spring biased brake shoes to engage the drum, causing an immediate halt to the tool motion. The present invention is an improvement thereover in that no solenoid is necessary thereby eliminating a cost factor and as a further advantage, the mechanism is relatively simple and maintenance free.
Also of interest is U.S. Pat. No. 1,502,169 to C. B. Bennett which discloses a rotary tool having a saw type handle with a linkage connected to an electric switch for starting and stopping the motor. The patent does not disclose a cam element for expanding spring biased brakes positioned about a brake drum.
Other prior art patents in this general area include U.S. Pat. Nos. 3,096,453; 3,176,173; 3,579,066; 3,335,304 and 3,339,681. These patents are representative of the existing art in the general area of the present invention and are not intended to be an all inclusive listing of the prior art.
The present invention is an improvement over the prior art noted above in that the brake device may be readily incorporated in a wide variety of electric tools and is particularly suited for pistol-shaped electric tools which are activated by a trigger mechanism. The cam operation of spring biased brake shoes against the brake drum provides a safe immediate halt to the operation of the tool when pressure is released on the trigger. In electric drills, for example, the power may be cut off immediately when a drill breaks through the material thereby preventing the possibility of the drill getting away from the operator. Immediate stoppage is also important when operating tools such as electric saws for physical injury may result from continued rotation of the blade.